<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .color{
      background-color: red;
    }
  </style>
</head>
<body>
  <button class="color">按钮1</button>
  <button>按钮2</button>
  <button>按钮3</button>
  <button>按钮4</button>
<script>
  let btn = document.querySelectorAll('button');
  for(let i =0;i<btn.length;i++){
    btn[i].addEventListener('click',function(){
      document.querySelector('.color').className = ''
      this.className = 'color'
    })
  }


</script>
</body>
</html>